Is Your Brake Fluid Contaminated?

Hi, welcome to Charlie's Garage. Today what we're going to talk about is brake fluid and I know that on a lot of my videos I'm talking about heavy duty trucks and most of the time we're dealing with air brakes and I've done videos in the past with air compressors and stuff but there are a lot of heavy duty trucks class 5, 6 even some I think some 7 trucks that might have hydraulic brakes. So even a heavy equipment mechanic who deals mostly with air brakes might still need to have a working understanding of how hydraulic brakes work and so this video is just going to be about brake fluid basics. So brake fluid is basically comes in different types of DOT 3, DOT 4, DOT 5, DOT 5.1 and really the big differences between all these are the chemical makeup of them so you have a glycol setup all the way up to the 5.1s which use a silicone setup and the boiling points differ from type to type. So the brake fluid is responsible for some major things. Number one thing is the obvious one right is that it transmits force. When you step on the master cylinder you push against fluid that fluid goes to the calipers and pushes on the brake shoes and pushes them against the rotor right and so that's the number one thing it does is it transmits the pressure to apply the brakes. While it does that it also helps to cool things down carries heat away it lubricates components in that system but the main point of this video is the thing that it does is that it absorbs moisture right so when we talk about absorbing moisture what we mean is that when you have condensation and other things that get into the brake fluid that water gets in there and it affects the way the brake fluid operates. So what we have to worry about is when you start to get water in the brake fluid what that does is it reduces or lowers the boiling point of the brake fluid. So I wrote down a couple key numbers here for us of the difference between dot three and dot five and what the boiling points are on those and when you look at a brake fluid specification you're going to have a dry boiling point and a wet boiling point and a dry boiling point is what it should take for the brake fluid to boil straight out of the bottle with no outside moisture being introduced to it yet. The wet boiling point is based on a 3.7 absorption of water so up to a 3.7 percent of the brake fluid being moisture that it's absorbed you know so the brake fluid wants to absorb that moisture so that moisture doesn't cause corrosion and and other issues in the system but the negative of that is the fact that it affects the boiling point of the actual brake fluid. You can get to temperatures excuse me between 400 and 500 degrees at your calipers so that means that brake fluid obviously can't boil at your normal you know 212 degrees it needs to be able to get much hotter than that otherwise it would boil and that would cause some serious issues in the brake system right and normal boiling point for dry boiling point for dot three is around 401 degrees so that's pretty hot right it can get pretty hot before it starts to boil but when it absorbs that 3.7 percent of moisture that can drop all the way down to 284 degrees right so you can see what a drastic difference just a 3.7 percent absorption of water can do to that boiling point for the dot three so 401 dry 284 wet the dot five is 500 degrees fahrenheit dry and 356 degrees fahrenheit wet so the dot five is able to still get pretty hot even with some moisture in it so a lot of times you might be working on a car or truck that has spongy inefficient braking and it's not stopping very well and what happens is that you might think oh well i got air in the line so you bleed it a lot and you still get that spongy feel to it it's not feeling right you gotta keep in mind that it could be moisture content in the brake fluid because what happens is something called evaporation i don't know if evaporation is really the right word vaporization i think is the better word to use with this so when the water gets into that brake fluid it allows it to actually vaporize and when it vaporizes that's what allows compression of the fluid and that's what gives you that spongy feel and that inefficient braking so one of the ways that you can tell and my friends at testament are the ones that inspired this video by sending me this tool and this is a very cool tool to use and they're very affordable but they're moisture detectors for brake fluid so for example for this one i have some brake fluid in a container where i put a little bit of brake fluid in one and a little bit in one that has water in it so what i'm going to do is i'm going to put some brake fluid right here in this guy and this is pure brake fluid and we're going to test the brake fluid by itself so the the testament indicator right here and i will put a link to this product in there just so you guys know where i got it because these guys are really cool about sending it to me you just turn it on and then once you turn it on it has features for picking what kind of brake fluid you have and i know it's hard to see but i can choose between dot three dot four dot five excuse me so right now i've got it selected for dot three we're going to just go ahead and this is a flexible tip so i'm going to adjust this so that you guys can see the readout put it in here so it's telling me 2.5 percent 2.2 to 2.5 you notice it was flashing in the green which means that the absorption is still within specification for what it's allowed to have right so now we're going to replace this one we'll clean the tip off real well which you should always do when you use a tool like this between use a shop towel lint-free cloth clean it up real well before you put stow it away or before you use it on another sample so now i've got the one that i introduced a little bottle of water put a little cap full of water in there so it's the same little size of a container the bottom of a styrofoam cup with a cap full of water added to the brake fluid so when i do the same thing with this one though um i should see a very different result because that cap full fluid is a pretty high percentage for his little brake fluid that's in this okay and i can see right now it's reading red and it says out of limits so this will automatically tell you when you've gone above your maximum allowable water absorption so this is a very quick and easy way to see hey i can bleed this thing to death it's not going to make a difference i need to flush and change my brake fluid so uh this is a tool that if you're going to be doing a hydraulic brake work uh testman makes these and a lot of different types and models you go to their amazon page uh testman t-s-t-e-s-m-e-n uh they they make a lot of these so you can get a version like this one which is really affordable and can do almost all the testing you're really going to need to do um and then you can also use test strips that will tell you some things but they're not quite as neat and accurate as this guy is so i hope you enjoyed this video i hope you learned a little bit about brake fluid uh one of the ways that we can test the brake fluid if you have any questions about uh brake fluid brakes in general or this test equipment please let me know in the comments please like and subscribe and please support our friends that send us tools to make videos about thank you